Ribosome biogenesis is a fundamental and energy intensive process for any growing or metabolically active cells. Complete loss of this process is incompatible with life. However, defects in ribosome biogenesis have been associated with a range of maladies including cancer and developmental diseases, termed ribosomopathies. One putative ribosomopathy with liver-specific defects is North American Indian Childhood Cirrhosis (NAIC), characterized by transient neonatal jaundice progressing to biliary cirrhosis. The only effective treatment is liver transplantation. Patients with this disease have an R565W mutation in the C-terminal region of human UTP4/Cirhin (hUTP4/Cirhin), a member of the t-UTP/UTPA subcomplex of the SSU processome, both of which are required for pre-rRNA transcription and processing. Our laboratory has previously shown that the C-terminus of hUTP4/Cirhin interacts with a novel, metazoan- specific ribosome biogenesis factor called NOL11. The R565W mutation disrupts the interaction between hUTP4/Cirhin and NOL11 leading us to hypothesize that the pathogenesis of NAIC is due to nucleolar dysfunction. SPECIFIC AIMS: The first aim will test the hypothesis that defective pre-rRNA processing contributes to the pathogenesis of NAIC. I will examine the effects of the R565W mutation on human pre- rRNA processing in cell culture and test the effect of the R565W mutation on protein-protein interactions within the t-UTP/UTPA subcomplex and SSU processome. As a complete understanding of all the t-UTP/UTPA subcomplex members is necessary for dissecting the pathogenesis of NAIC, I propose to discover the final unidentified human t-UTP/UTPA subcomplex analog of yeast Utp9. The nucleolar stress response is implicated in many other ribosomopathies. Therefore, I will test the hypothesis that the R565W mutation results in p53 induction. Since NAIC is a congenital disease, in the second aim I will establish Xenopus tropicalis as a model for the disease, allowing for the study of its pathogenesis within the context of a developing organism.